1. Technical Field
The present invention relates to a light-emitting device, and in particular to a semiconductor light-emitting device.
2. Reference to Related Application
This application is a continuation application of U.S. patent application, Ser. No. 12/292,593, entitled “Light-emitting device”, filed on Nov. 21, 2008, and the content of which is hereby incorporated by reference.
3. Description of the Related Art
The light-emitting mechanism and the structure of a light-emitting diode (LED) are different from that of the conventional light sources. The LED has advantages of small size and high reliability, and has been widely used in different fields such as displays, laser diodes, traffic lights, data storage apparatus, communication apparatus, lighting apparatus, and medical apparatus.
Referring to FIGS. 1A and 1B. FIG. 1A is the schematic top view of a conventional nitride-based light-emitting device 1, and FIG. 1B illustrates a cross-sectional view of the conventional nitride-based light-emitting device 1 along the A-A′ line in the FIG. 1A. The conventional nitride-based light-emitting device 1 includes a substrate 11, an n-type nitride-based layer 12, a light-emitting layer 13, a p-type nitride-based layer 14, a p-type transparent electrode 15, an n-type electrode 16 having the function as a bonding pad, and a p-type bonding pad 17. The p-type bonding pad 17 is used for current injection. The current is injected through the p-type bonding pad 17 and moves to and spread through the p-type transparent electrode 15. Electrons and holes recombine in the light-emitting layer 13 and then produce photons. In fact, as shown in FIG. 1B, the current is crowded in the area where the p-type transparent electrode 15 is close to the n-type electrode 16 to cause a poor light-emitting efficiency. Besides, the temperature in the current crowded area is so high that the life of conventional nitride-based light-emitting device 1 is reduced.
In order to resolve above problems, a known art disclosed a light-emitting device 2 which is illustrated by a top view as shown in FIG. 2. Another known art also disclosed a light-emitting device 3 which is illustrated by a top view as shown in FIG. 3. Referring to FIG. 2, the light-emitting device 2 includes a p-type electrode and an n-type electrode. The p-type electrode includes a p-type bonding pad 24, two first armed electrodes 24a extending from the p-type bonding pad 24, and second armed electrodes 24b interposed between two first armed electrodes 24a. The armed electrode can be used to decrease the light absorption of the p-type electrode. The current is injected from the p-type bonding pad 24 and spread by the armed electrodes. The n-type electrode includes an n-type bonding pad 25, third armed electrodes 25a, and fourth armed electrodes 25b. The current is injected from the p-type electrode, moves to the light-emitting region of the light-emitting device 2, and then flows to and out of the n-type electrode. The p-type armed electrodes 24a, 24b and the n-type armed electrodes 25a, 25b are interdigitated between each other.
Referring to the FIG. 3, the light-emitting device 3 includes an n-type electrode having a first contact 35 and an n-type fingered electrode 36 connected with the first contact 35 at a first side of the light-emitting device 3, a p-type electrode having a second contact 37 and two fingered electrodes 38a, 38b connected with the second contact 37 at a second side of the light-emitting device 3, wherein the first side and the second side are opposite to each other. The n-type fingered electrode 36 is extended from the first side to the second side, the p-type fingered electrodes 38a, 38b are extended from the second side to the first side, and the n-type fingered electrode 36 and the p-type fingered electrodes 38a, 38b are interdigitated between each other. The light-emitting devices 2 and 3 can resolve the current crowding and low light efficiency problems of the conventional light-emitting device 1 by the interdigitated extending electrodes.
Referring to FIG. 4, further another known art disclosed a light-emitting device 4. The epitaxial structure of the light-emitting device 4 includes a spiral-shaped trench, a p-type metal electrode 41 located in the exposed surface of the trench, an n-type metal electrode 42 located on the un-trenched surface of the epitaxial structure, a p-type bonding pad 43, and an n-type bonding pad 44, wherein the p-type metal electrode 41 and the n-type metal electrode 42 are parallel and distributed in spiral shape, which can resolve the current crowding and low light efficiency problems of the conventional light-emitting device 1
In above conventional light-emitting devices, the designs of electrodes adopt transparent electrodes or decrease the electrode area such as armed, fingered and spiral-shaped electrodes to optimize the light extraction area. In general, the width of an electrode is designed to be smaller than that of a bonding pad to avoid increasing the light absorption area of the electrode.